Send Orders of Reprints at
[email protected] Current Nanoscience, 2013, 9, 000-000
1
Enhanced Luminescent Properties of Solution Combustion Synthesized Nanocrystalline Y3Al5O12:Eu3+ Phosphors Sumei Wang1*, Xurong Zhao1, Shengming Zhou2 Limin Zhou3 and Guodong Xia3* 1
Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Shandong University, Jinan, P.R. China; Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, P.R. China; 3Department of Mechanical Engineering, the Hong Kong Polytechnic University, Kowloon, Hong Kong
2
Abstract: Nanocrystalline Y3Al5O12:Eu3+ phosphors with particle size about 20-40 nm have been synthesized by a facile solution combustion method. XRD and TEM studies show that Y3Al5O12 nanocrystals can directly form at a low temperature of 825 and highly crystalline at 850 . With the increase of annealing temperature, the charge transfer band shows a blue shift due to the dielectric confinement effect. The color purity of Y3Al5O12 :Eu3+ phosphors can be improved by decreasing the grain size of nanocrystals. Furthermore, the high concentration doping of Eu3+ can be realized in Y3Al5O12 nanocrystals, which will enhance the luminescent intensity. This work demonstrated that solution combustion is a feasible method to synthesize europium rare earth doped Y3Al5O12 nanocrystals with enhanced optical properties.
Keywords: Nanocrystalline, combustion synthesis, Y3Al5O12: Eu3+ phosphors, luminescence. 1. INTRODUCTION In the recent years, various functional nanomaterials, such as nanoparticles, nanotubes, nanoporous materials, and nanofilms have been developed [1-4]. Among them, rare earth doped luminescent materials have gained huge interest due to a variety of applications including phosphors for fluorescent lighting, display monitors, amplifiers in optical telecommunication and lasers [5-7]. Y3Al5O12 doped with rare earth element can be widely used as solid-state laser materials in the luminescence field and window materials for a variety of lamps [8-11]. Y3Al5O12:Eu3+ red phosphors are used for cathode ray tube screens and high-definition projection televisions. Furthermore, Y3Al5O12:Eu3+ can also be used as fluorescence thermometry due to its sensitive temperature-dependent characteristics [12]. Practical application of these materials has revealed several unexpected drawbacks, such as short-term degradation, poor color quality, and low luminous intensity [13]. An improvement performance of lamps and displays has an urge need for phosphors with enhanced optical properties. As is well known that grain size, morphology, agglomeration, and surface passivation have significant influences on the phosphor performance. These factors are related to the synthesis method, which is a recent orientation for the development of high-quality phosphors. The conventional procedure to synthesize Y3Al5O12 phosphors is based on solid state reactions. It requires high annealing temperature of 1600 to obtain pure phase, which usually produce agglomerated powders with grains of micrometer size [14-16]. Various preparation methods have been developed to lower annealing temperature and obtain small particle size of phosphors [17-19]. In particular, combustion synthesis is a relatively fast and economical way to obtain phosphors with nanometric particle size. It involves a self-sustaining exothermic process between metal nitrates and an organic fuel [20-23]. Recently, some solution combustion methods have been employed to synthesize Y3Al5O12:Eu3+ phosphors [2427]. However, the Eu3+ luminescence in the Y3Al5O12 lattice is mainly orange color instead of pure red color, which limits its wide *Address correspondence to this author at the Key Laboratory for LiquidSolid Structural Evolution and Processing of Materials, Shandong University, Jinan, P. R. China; Tel: 86-531-88392439; Fax: 86-531-88392439; E-mails:
[email protected];
[email protected] 1573-4137/13 $58.00+.00
application in tricolor display system. In the present paper, Y3Al5O12:Eu3+ nanocrystal phosphors are synthesized by the solution combustion method with the citrate complexing agent, affording 20-40 nm nonaggregated particles. The obtained highly crystallined Y3Al5O12:Eu3+ powder possess high luminescence intensity. The relationship between microstructure and luminescence properties of Y3Al5O12:Eu3+ nanocrystals was also investigated. We found that the color purity of Y3Al5O12:Eu3+ phosphors can be improved by decreasing the grain size of nanocrystals. Furthermore, the high concentration doping of Eu3+ in Y3Al5O12 nanocrystals will enhance the luminescence intensity. These promising results would contribute to the development of high performance rare earth oxide nanophosphors. 2. EXPERIMENTAL SECTION Y3Al5O12:Eu3+ nanocrystals were prepared by the citrate combustion method, involving the exothermic reaction between metal nitrate and organic fuel citric acid. The combustion can be represented as: 9(1-x)Y(NO3)3+ 15Al(NO3)3+9xEu(NO3)3+20C6H8O73(Y1-xEux)3 Al5O12+36N2+120CO2+ 80H2O In a typical preparation procedure, Eu(NO3)3 solution was prepared by dissolving 1mmol high-purity Eu2O3 with HNO3 and some deionized water. 16.7 mmol Al(NO3)39H2O, 9 mmol Y (NO3)36H2O were dissolved in deionized water to obtain 0.1 mol/l solution. 24 mmol citric acid was then added to form complex citrates of corresponding metal ions. After the clear solution was formed through uniform stirring, NH4OH solution was added into the mixture to adjust the PH of solution to be 4-5. The combustion of citrate precursors was carried out in an oven at about 250 , and then the yellowish powder was annealed at 800-850 . Powder X-ray diffraction (XRD) patterns were obtained with a Rigaku D/MAX-2550 diffractometer (Cu K radiation). Fourier infrared (FTIR) spectra were recorded on a Fourier transform Nicolet NEXUS 870 spectrometer. Transmission electron microscopy (TEM) was performed using a JEOL JEM 2010F microscopy. High resolution TEM images were observed with JEOL JEM2010F operating at 300 kV. The excitation and emission spectra were obtained by a JASCO FP-6500 fluorescence spectrophotometer.
© 2013 Bentham Science Publishers
2 Current Nanoscience, 2013, Vol. 9, No. 2
Wang et al.
3. RESULTS AND DISCUSSION (Fig. 1) show XRD patterns of Y3Al5O12:Eu3+ phosphors annealed at 800-850 . The weak peak centered at 33.3° at 800 is corresponding to the (420) plane of cubic garnet phase. The samples annealed at 825 and 850 are indexed as Y3Al5O12 phase (JCPDS file 33-40) without other detectable phases. The average crystallite size (Table 1), calculated with Scherrer’s formula, increases from 20 nm to 35 nm as annealing temperature increases from 800 to 850 . The FTIR spectra of Y3Al5O12:Eu3+ phosphors are presented in (Fig. 2). A sharp band around 2349 cm-1 originates from the trace of CO2 trapped in the combustion products. Two absorption bands at 1537 and 1405 cm-1 are attributed to COO stretch and N-O stretch, respectively. With the increase of annealing temperature, these organic groups gradually pyrolyze. The characteristic absorption bands related to these organic groups disappear at the temperature of 825 , and metal-oxygen absorption bands began to occur. The bands at 790 and 683 cm-1 are Al-O stretch, and those at 724 and 453 cm-1 are Y-O stretch. The appearance of these metal-oxygen absorption bands also indicates that Y3Al5O12 phase has formed. Obviously, the Y3Al5O12 phase begins to crystallize at 800 , and has completely formed at 825 , which is about 800 lower than that required for the solid state reaction (1600 ). It is well known that citric acid is a complexation agent, not only limiting the particles size of the Y3Al5O12:Eu3+ phosphors, but also increasing their stability. Since citric acid can easily complex a number of metal ions, the citrate combustion method can prepare nanoscale particles of metal oxides This method has been applied to synthesize many nanocrystals of metal oxide [28-30]. In the sol-gel process, citric acid forms a polymeric network to hinder cations mobility and maintain local stoichiometry, primarily responsible for the lowered the crystallization temperature of Y3Al5O12 phase. Another function of citric acid is the potential heat of combustion, which also facilitates the rapid crystallization.
sponge-like structure with many pores, which are mainly attributed to the large amount of gas byproducts during the combustion reaction. In contrast, the Y3Al5O12:Eu3+ phosphors at 825-850 almost appear to be sphere and nonaggregated nanoparticles. The average grain size of Y3Al5O12 phosphors at 825 and 850 is about 30 and 40 nm, respectively, which is close to the average crystallite sizes of 26 nm and 35 nm estimated by Scherrer’s formula. The high-resolution TEM images of the Y3Al5O12:Eu3+ nanocrystals are shown in (Fig. 4). For the nanocrystals annealed at 825 , the surface is made up of two structural components. The major part is well-crystallized core with long-range order, and the other is disordered grain boundary or amorphous part. Defects tend to migrate to the surface of the crystal during the growth stage [31]. However, the surface of Y3Al5O12:Eu3+ nanocrystals annealed at 850 is highly crystalline, and free from surface defect layer, which indicates that the surface defects of Y3Al5O12:Eu3+ nanocrystals can be removed by thermal annealing with a slightly higher temperature. Therefore, solution combustion method could effectively synthesize highly crystalline phosphor materials at a relatively low temperature due to the self-generated heat.
Fig. (2). FTIR spectra of Y 3Al5O12 : Eu3+ phosphors annealed at 800-850 . (a) 800 ; (b) 825 ; (c) 850 .
Fig. (1). XRD patterns of Y3Al5O12 :Eu3+ phosphors annealed at 800-850 . (a) 800 ; (b) 825 ; (c) 850 .
Table 1. The Intensity Ratio of Y3Al5O12:Eu3+ Phosphors
5
D07F2 to
5
D07F1 for
D0 7F1
Intensity Ratio
26.9
18.4
1.47
26
25.7
74.4
0.35
35
69.6
243.1
0.28
Annealing Temperature()
Grain Size (nm)
800
20
825 850
D0 7F2
5
5
Fig. (3). TEM images of Y3Al5O12:Eu 3+ phosphors annealed at 800-850 . (a) 800 ; (b) 825 ; (c) 850 .
Fig. (3) shows TEM images of Y3Al5O12:Eu3+ phosphors annealed at 800-850 . The Y3Al5O12:Eu3+phosphors at 800 are
Fig. (4). High resolution TEM image of Y 3Al5O12 :Eu3+ phosphors. (a) at 825 ; (b) at 850 .
Enhanced Luminescent Properties of Solution Combustion Synthesized
Current Nanoscience, 2013, Vol. 9, No. 2
3
Fig. (5). Excitation and emission spectra of Y3Al5O 12:Eu3+ phosphors. (a) 800 ; (b) 825 ; (c) 850 . (d) The energy level diagram of Eu3+ ion.
Fig. (5) exhibits the excitation and emission spectra of Y3Al5O12:Eu3+ phosphors. The excitation spectra mainly consist of the charge transfer band of Eu3+ and f-f transitions within Eu3+ 4f6 configuration. The environment of Eu3+ ions changes from site to site in the amorphous phosphors, which leads to the much broader charge transfer band. As the phosphors crystallize, the charge transfer band becomes sharper and shifts to higher energy. It is clear that the charge transfer band shows a blue shift with the increase of annealing temperature, which is related to the dielectric confinement effect [32]. With the increase of the annealing temperature, less hydroxyl groups will be adsorbed onto the surfaces of Y3Al5O12:Eu3+ nanocrystals, which were verified by FTIR results. The modified surfaces of Y3Al5O12:Eu3+ nanocrystals might lead to the formation of a surface state energy band, which caused blue shift due to dielectric confinement effect. The emission spectra consists of sharp peaks from 550 to 650 nm, corresponding to the transitions from the excited 5D0 level to 7FJ (J=1–4) levels of Eu3+ ions [33]. The related electric dipole transitions of Eu3+ ion along with the energy level diagram are shown in (Fig. 5d). The emission peak at 614 nm is due to forced electric dipole transition of 5 D07F2, a characteristic red emission. Whereas, the strong emission peak of nanocrystalline Y3Al5O12:Eu3+ phosphors is related to 5 D07F1 transition centered at 592 nm and 598 nm. The color of crystalline Y3Al5O12:Eu3+ phosphors is mostly in orange emission, which is not pure enough as compared to the red color of amorphous counterparts. The inferior color purity of crystalline phosphor limits its application for display and luminescence device. For applications, it is required that the main emission is concentrated on the 5D07F2 transition around 610–630 nm. If rare earth ions occupy sites with inversion symmetry, 5D07F1 transitions will be relatively strong. On the contrary, more emission will be observed in 5D07F2 transitions when Eu3+ ions occupy sites with no inversion symmetry [34]. The intensity ratio of 5D07F2 to 5 D07F1 transition can be viewed as a clue concerning the nature of the chemical surroundings of the luminescent centre and its symmetry [18]. The relationship between values of this intensity ratio and annealing temperatures is listed in (Table 1). A sharp decrease of the intensity ratio from amorphous to crystalline phosphors reflects the change of the local surroundings for the luminescent center during the transformation from amorphous state to crystalline one. An interesting phenomenon is that the luminescent intensity ratio of nanocrystals increases as the grain size decreases, which should be related to the microstructure of nanocrystals. As grain size decreases, the degree of disorder increases, as is shown in (Fig. 4), and the local symmetry of Eu3+ ion lowers, which will increase the transition ratio of 5D07F2 and enhance the red emission. It is evident that the color purity of Y3Al5O12:Eu3+ nanocrystals can be improved by decreasing the grain size. Similar results were also observed in YBO3:Eu3+ nanocrystals [35].
Compared with bulk phosphors, one major drawback of nanocrystalline phosphors is their low luminescence intensity, which is related to the character of nanocrystals. The drastically enlarged ratio of surface to volume and surface defects favoring recombination is responsible for the decrease of the emission intensity in nanometer materials [36]. The luminescence intensity of Y3Al5O12:Eu3+ nanocrystals can be improved through optimization of Eu3+ concentrations. Here, the Y3Al5O12:Eu3+ nanocrystals at 850 are taken as an example, and the relationship between emission intensity and Eu3+ concentrations is shown in (Fig 6). It can be seen that Eu3+ can be doped up to 14 in Y3Al5O12 nanocrystals without fluorescence quenching observed. The Eu3+ quenching concentration in our Y3Al5O12:Eu3+ nanocrystals is much higher than the normal quenching concentration of 6–8 % [37]. It is well known that liquid routes, in particular the sol-gel process, yield products with residual hydroxyl groups. These hydroxyl groups are very efficient quenchers of the luminescence via nonradiative processes due to their high-energy vibration mode (~3500 cm-1), which will give rise to the low emission intensity [13,38]. However, the vibration band of hydroxyl groups in Y3Al5O12:Eu3+ phosphors synthesized by solution combustion is too broad and weak to be observed as a band, as shown in (Fig 2). Existence of few residual hydroxyl groups in Y3Al5O12:Eu3+ phosphors by solution combustion method will increase the luminescence intensity. Moreover, the solution combustion method provides a uniform distribution of Eu3+ in the Y3Al5O12 nanocrystalline host, and enhances the quenching concentration and luminescence intensity.
Fig. (6). The emission intensity (monitored by 5D07F1 transition) of Y3Al5O 12:Eu3+ phosphors at 850 .
4 Current Nanoscience, 2013, Vol. 9, No. 2
Wang et al.
4. CONCLUSIONS The synthetic method for Y3Al5O12:Eu3+ nanocrystalline phosphors presented in this paper is a simple and efficient solution combustion process. The crystallization temperature of Y3Al5O12 phase is significantly lowered, compared to that of the solid state reaction. TEM results show that Y3Al5O12:Eu3+ nanocrystals at 850 are highly crystalline. A more pure red emission can be obtained by decreasing the grain size. The high concentration quenching in Y3Al5O12:Eu3+ nanocrystalline phosphors leads to the high luminescence intensity. It indicates that Y3Al5O12:Eu3+ nanocrystals synthesized by solution combustion are potential red phosphors with enhanced luminescence properties. CONFLICT OF INTEREST The authors confirm that this article content has no conflicts of interest. ACKNOWLEDGEMENTS This work was supported by the National Natural Science Fountain of China (No. 61106086), the Promotive research fund for excellent young and middle-aged scientisits of Shandong Province (BS2011DX014)Independent Innovation Foundation of Shandong University (IIFSDU, No. 31370071614010) and Hong Kong PolyU Postdoctoral Fellowship Project (G-YX4Y).
[15] [16]
[17] [18]
[19] [20]
[21]
[22]
[23]
[24]
REFERENCES [1]
[2]
[3] [4]
[5] [6] [7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
Zhang, R. Y.; Khalizov, A.; Wang, L.; Hu, M.; Xu, W. Nucleation and Growth of Nanoparticles in the Atmosphere. Chem. Rev., 2012, 112, 19572011. Lu, W. B.; Zu, M.; Byun, J. H.; Kim, B. S.; Chou, T. W. State of the Art of Carbon Nanotube Fibers: Opportunities and Challenges. Adv. Mater., 2012, 24, 1805-1833. Ariga, K.; Vinu, A.; Yamauchi, Y.; Ji, Q. M.; Hill, J. P. Nanoarchitectonics for Mesoporous Materials. B. Chem. Soc. Jpn., 2012, 85, 1-32. Ariga, K.; Ji, Q. M.; Hill, J. P.; Bando, Y.; Aono, M. Forming nanomaterials as layered functional structures toward materials nanoarchitectonics. Npg Asia Mater., 2012, 4-7. Rohwer, L. S.; Martin, J. E. Measuring the absolute quantum efficiency of luminescent materials. J. Lumin., 2005, 115, 77-90. Do, Y. R.; Bae, J. W. Application of photoluminescence phosphors to a phosphor-liquid crystal display. J. Appl. Phys., 2000, 88, 4660-4665. Xu, X. D.; Zhao, Z. W.; Song, P. X.; Zhou, G. Q.; Xu, J.; Deng, P. Z. Growth and optical properties of a new self-Q-switched laser crystal: Cr4+:Yb3Al 5O12 . Solid State Commun., 2004, 129, 717-720. Purwanto, A.; Wang, W. N.; Ogi, T.; Lenggoro, I. W.; Tanabe, E.; Okuyama, K. High luminance YAG:Ce nanoparticles fabricated from urea added aqueous precursor by flame process. J. Alloy. Compd., 2008, 463, 350-357. Xu, X. D.; Zhao, Z. W.; Song, P. X.; Xu, J.; Deng, P. Z. Growth of highquality single crystal of 50at.%Yb:YAG and its spectral properties. J. Alloy. Compd., 2004, 364, 311-314. Xia, G.; Zhou, S.; Zhang, J.; Wang, S.; Xu, J. Solution combustion synthesis, structure and luminescence of Y3Al5O12:Tb3+ phosphors. J. Alloy. Compd., 2006, 421, 294-297. Xia, G.; Zhou, S.; Zhang, J.; Xu, J. Structural and optical properties of YAG:Ce3+ phosphors by sol-gel combustion method. J.Cryst. Growth, 2005, 279, 357-362. Allison, S. W.; Gillies, G. T. Remote thermometry with thermographic phosphors: Instrumentation and applications. Rev. Sci. Instrum., 1997, 68, 2615-2650. Nedelec, J. M.; Avignant, D.; Mahiou, R. Soft chemistry routes to YPO4based phosphors: Dependence of textural and optical properties on synthesis pathways. Chem. Mater., 2002, 14, 651-655. Yang, H. K.; Jeong, J. H. Synthesis, Crystal Growth, and Photoluminescence Properties of YAG:Eu3+ Phosphors by High-Energy Ball Milling and SolidState Reaction. J. Phys. Chem. C, 2010, 114, 226-230.
Received: ?????? 28, 2011
Revised: ?????? 22, 2012
Accepted: ????? 6, 2012
[25]
[26]
[27]
[28]
[29]
[30] [31] [32]
[33]
[34]
[35]
[36] [37] [38]
Yu, J.; Chen, Y.; Glushenkov, A. M. Titanium Oxide Nanorods Extracted From Ilmenite Sands. Cryst. Growth Des., 2009, 9, 1240-1244. Dong, G. P.; Xiao, X. D.; Chi, Y. Z.; Qian, B.; Liu, X. F.; Ma, Z. J.; Wu, E.; Zeng, H. P.; Chen, D. P.; Qiu, J. R. Size-dependent polarized photoluminescence from Y3Al5O12:Eu3+ single crystalline nanofiber prepared by electrospinning. J. Mater. Chem., 2010, 20, 1587-1593. Hreniak, D.; Strek, W. Synthesis and optical properties of Nd3+-doped Y3Al5O12 nanoceramics. J. Alloy. Compd., 2002, 341, 183-186. Lu, C. H.; Hsu, W. T.; Dhanaraj, J.; Jagannathan, R. Sol-gel pyrolysis and photoluminescent characteristics of europium-ion doped yttrium aluminum garnet nanophosphors. J. Eur. Ceram. Soc., 2004, 24, 3723-3729. Aruna, S. T.; Mukasyan, A. S. Combustion synthesis and nanomaterials. Curr. Opin. Solid St. M., 2008, 12, 44-50. Capobianco, J. A.; Vetrone, F.; D'Alesio, T.; Tessari, G.; Speghini, A.; Bettinelli, M. Optical spectroscopy of nanocrystalline cubic Y2O3:Er3+ obtained by combustion synthesis. Phys. Chem. Chem. Phys., 2000, 2, 32033207. Polizzi, S.; Bucella, S.; Speghini, A.; Vetrone, F.; Naccache, R.; Boyer, J. C.; Capobianco, J. A. Nanostructured lanthanide-doped Lu2O3 obtained by propellant synthesis. Chem. Mater., 2004, 16, 1330-1335. Xia, G.; Wang, S.; Zhou, S.; Xu, J. Selective phase synthesis of a high luminescence Gd2O3:Eu nanocrystal phosphor through direct solution combustion. Nanotech., 2010, 21, 345601. Xia, G.; Zhou, S.; Zhang, J.; Wang, S.; Xu, J. Direct synthesis and intense luminescence of Y2O3:Eu nanophosphors by complexation combustion. Chem. Lett., 2005, 34, 1166-1167. Zhou, Y. H.; Lin, J.; Wang, S. B.; Zhang, H. J. Preparation of Y3Al5O12:Eu phosphors by citric-gel method and their luminescent properties. Opt. Mater., 2002, 20, 13-20. Guo, K.; Zhang, X. M.; Chen, H. H.; Yang, X. X.; Guo, X.; Zhao, J. T. Influence of fuels on the morphology of undoped Y3Al5O12 and photoluminescence of Y3Al5O12:Eu3+ prepared by a combustion method. Mater. Res. Bull., 2010, 45, 1157-1161. Hsu, W. T.; Wu, W. H.; Lu, C. H. Synthesis and luminescent properties of nano-sized Y3Al5O12:Eu3+ phosphors. Mat. Sci. Eng. B-Solid, 2003, 104, 4044. Xia, G.; Zhou, S.; Zhang, J.; Wang, S.; Liu, Y.; Xu, J. Sol-gel combustion synthesis and luminescent properties of nanocrystalline YAG:Eu3+ phosphors. J. Cryst. Growth, 2005, 283, 257-262. Wu, K. H.; Huang, W. C. Effect of varying the acid to metal ion ratio R on the structural and magnetic properties of SiO2-doped Ni-Zn ferrite. J. Solid State Chem., 2004, 177, 3052-3057. Jacobsohn, L. G.; Bennett, B. L.; Muenchausen, R. E.; Tornga, S. C.; Thompson, J. D.; Ugurlu, O.; Cooke, D. W.; Sharma, A. L. L. Multifunction Gd2O3:Eu nanocrystals produced by solution combustion synthesis: Structural, luminescent, and magnetic characterization. J. Appl. Phys., 2008, 103, 104303. Mahata, I.; Das, G.; Mishra, R. K.; Sharma, B. P. Combustion synthesis of gadolinia doped ceria powder. J. Alloy. Compd., 2005, 391, 129-135. Wakefield, G.; Holland, E.; Dobson, P. J.; Hutchison, J. L. Luminescence properties of nanocrystalline Y2O3:Eu. Adv. Mater., 2001, 13, 1557-1560. Zhang, Y. W.; Si, R.; Liao, C. S.; Yan, C. H. Facile alcohothermal synthesis, size-dependent ultraviolet absorption, and enhanced CO conversion activity of ceria nanocrystals. J. Phys. Chem. B, 2003, 107, 10159-10167. Wen, F. S.; Chen, J. S.; Moon, J. H.; Kim, J. H.; Niu, J. H.; Li, W. L. Hydrothermal synthesis and luminescent properties of Sb3+-doped Sr3[PO4]2. J. Solid State Chem., 2004, 177, 3114-3118. Xia, G.; Zhou, S.; Zhang, J.; Wang, S.; Wang, H.; Xu, J. Sol-gel combustion synthesis and luminescence of Y4Al2O9:Eu3+ nanocrystal. J. Non-Crystalline Solids, 2005, 351, 2979-2982. Wei, Z. G.; Sun, L. D.; Liao, C. S.; Yan, C. H. Fluorescence intensity and color purity improvement in nanosized YBO3:Eu. Appl. Phys. Lett., 2002, 80, 1447-1449. Feldmann, C. Polyol-mediated synthesis of nanoscale functional materials. Adv. Funct. Mater., 2003, 13, 101-107. Shi, S. K.; Wang, J. Y. Combustion synthesis of Eu3+ activated Y3Al5O12 phosphor nanoparticles. J. Alloy. Compd., 2001, 327, 82-86. Huignard, A.; Gacoin, T.; Boilot, J. P. Synthesis and luminescence properties of colloidal YVO4:Eu phosphors. Chem. Mater., 2000, 12, 1090-1094.
